Wheel slip control system for vehicles with electric brakes

ABSTRACT

A wheel slip control system for a wheeled vehicle having an electrically operated brake for at least one wheel thereof and an electric brake controller for modulating the actuation of the brake which includes a wheel speed sensor for the wheel, a detector for detecting an incipient excessive slip condition, and means for relieving brake actuation upon the detected occurrence of an incipient excessive slip condition.

United States Patent 1 Podlewski et al.

[ WHEEL SLIP CONTROL SYSTEM FOR VEHICLES WITH ELECTRIC BRAKES Inventors:Robert S. Podlewski, Jackson;

William T. Birge, Plymouth, both of Mich.

Kelsey-Hayes Company, Romulus, Mich.

Filed: Sept. 13, 1971 Appl. No.: 179,858

Assignee:

[52] US. Cl 303/21 EB, 188/3 R, 303/7,

Int. Cl B60t 8/10 Field of Search 188/3 R, 181 C;

References Cited UNITED STATES PATENTS 1/1969 Beltramo 303/20 X PrimaryExaminerMilton Buchler Assistant ExaminerStephen G. KuninAtt0rneyl-larness, Dickey & Pierce [57] ABSTRACT A wheel slip controlsystem for a wheeled vehicle having an electrically operated brake forat least one wheel thereof and an electric [brake controller formodulating the actuation of the brake which includes a wheel speedsensor for the wheel, a detector for detecting an incipient excessiveslip condition, and means for relieving brake actuation upon thedetected occurrence of an incipient excessive slip condition.

3 Claims, 1 Drawing Figure Jerrjar PAIENIEUMC 1 1 191a m wy v .N\

WHEEL SLIP CONTROL SYSTEM FOR VEHICLES WITH ELECTRIC BRAKES BACKGROUNDAND SUMMARY OF THE INVENTION The present invention relates to a wheelslip control system, and more particularly, to a wheel slip controlsystem for a vehicle having an electric brake such as a trailer or othertowed vehicle. Typically, a towed vehicle may have one or more pairs ofwheels with an electric brake for each wheel which includes a brake shoeor brake pad which is operated by an electromagnetic device. Theelectromagneticdevice is energized to operate the brakes by a connectionto the towing vehicle battery through a brake controller whichordinarily consists of a variable potentiometer located in the towingvehicle. The brake controller is effective to vary the current throughthe electromagnetic device so as to vary an engaging force between thebrake shoe or pad and an opposed friction surface such as a brake drumor disc, respectively.

It will be well appreciated by those skilled in the art that the typicalconnection between a towing vehicle and a towed vehicle is a singlepoint universal connection which permits a large degree of relativeangular movement between the towing vehicle and the towed vehicle.Accordingly, it is important that the towed vehicle be stable during allphases of operation. The stability of a towed vehicle is especiallycritical during a maximum braking condition since, under someconditions, the wheels of the towed vehicle may lock, and consequently,the towed vehicle may tend to overrun the towing vehicle to create whatis commonly referred to as a jack-knifed condition. I

It is an object of this invention toprovide a wheel slip control systemfor a towed vehicle having electric brakes which augments the stabilityof the towed vehicle during a braking condition to prevent jack-knifing,or other undesirable motions or forces between the towing vehicle andthe towed vehicle. This is accomplished by providing a wheel slipcontrol system for the towed vehicle which senses an incipient excessiveslip condition at one or more of the wheels and which is connected tothe circuit providing electrical energy to operate the brake actuatorsin a manner to relieve brake actuation upon the detection of anincipient excessive slip condition, and to reinstate brake actuationafter the wheels have spun-up to a controlled slip condition. In itspreferred form, the system relieves brake actuation when an incipientexcessive slip condition exists at any one wheel and reinstates brakeactuation after the last wheel has spun-up to a controlled slipcondition.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematic illustrationof an exemplary wheel slip control system according to the presentinvention for a vehicle having electrically actuated brakes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, a wheelslip control system is shown for a vehicle having electrically actuatedbrakes 12 and 14. The brakes l2 and 14 are associated with aconventional brake controller 20 and conventional electromagneticactuators 22 and 24, respectively. The

actuators 22 and 24 are connected in parallel so as to equally receivecurrent passing through the brake controller 20 from the positiveterminal 26 of the towing vehicle battery. The circuit is completed toground through a normally-conducting transistor Q5. The actuator 20 isof the variable potentiometer type so that it is effective to vary thelevel of current delivered to the electromagnetic actuators 22 and 24 byadjustment of the total impedance in the current path. The brakecontroller 20 may be mounted in the towing vehicle so as to be operatedbydepression of the towing vehicle brake pedal and/or may be providedwith a lever for manual control of the brakes of the towed vehicle.

The brakes 12 and 14 for the towed vehicle may be drum brakes asillustrated or may be disc brakes. In the former type, brake shoes 28are utilized, each of which carry an electromagnetic coil essentiallycomprising each of the actuators 22 and 24, and are so designed so astocause an electromagnetic attraction between the shoes 28 and the brakedrums 30 which is effective to establish an engaging force between thefriction linings of the brake shoes 28 and the drums 30 which isproportional or related to the current through the actuators 22 and 24.It is important to note that the actuators 22 and 24 are not onlyelectrically controlled in accordance with the level of the current, butare also operated, i.e., powered or motivated, electrically by virtue ofthe flow of current through the electromagnetic actuators 22 and 24.

In the exemplary system shown in the FIGURE, a right wheel of the towedvehicle is provided with a wheel speed sensor 32 and a left wheel of atowed vehicle is provided a wheel speed sensor 34. The wheel speedsensors 32 and 34 provide a train of pulses, which are numericallyrelated to the angular displacement of the wheel, to integrators 36 and38, respectively, which integrate the train of pulses from the wheelspeed sensors 32 and 34 to provide signals on the integrator outputlines 40 and 42 which are representative of the instantaneous speed ofthe respective wheels. The signals on line 40 and 42 are supplied to acircuit 44 which is responsive to the wheel speed signal having theleast magnitude and provides an output signal at terminal 46 which isrepresentative of the wheel speed of the slowest wheel. Morespecifically, the output signal on line 40 representative of the rightwheel speed is delivered to the base of a transistor O1 to turn on thetransistor Q1 and to modulate the output of the transistor Q1 if thesignal on line 40 is less than the voltage at the emitter of transistorQ1. Similarly, the signal on line 42 representative speed of the leftwheel is delivered to the base of the transistor O2 to turn on thetransistor Q2 and to modulate the output of the transistor Q2 when thesignal level falls below the voltage at the emitter of transistor 02.Assuming now that an excessive slip condition is encountered so that theleft wheel first enters into an excessive slip condition so that speedof the left wheel falls below the speed of the right wheel, the leftwheel speed signal on line 42 will fall below the potential at theemitter of Q2 soas to turn on the transistor Q2 thereby lowering thepotential at the terminal 46 to a magnitude in accordance with the leftwheel speed signal on line 42. The potential at the terminal 46 (alsothe potential at the emitter of transistor O1) is reduced to a magnitudewhich is less than the magnitude of the right wheel speed so that thetransistor O1 is maintained in a non-conductive condition. Consequently,the transistor Q2 solely controls the potential at terminal 46. It willbe appreciated that the potential at the terminal 46 will be varied inaccordance with the instantaneous speed of the excessively slipping leftwheel so as to be representative thereof. Conversely, if the right wheelis first to enter an excessive slip condition, the transistor Q1 willcontrol the potential at terminal 46. The signal at line 46 is amplifiedby an emitter-follow or transistor Q3 to provide an amplified signal online 48 representative of the speed of the wheel having the slowestwheel speed. The signal on line 48 is received by an excessive slipdetecting circuit 50 which detects an incipient excessive slip conditionand provides an output signal on line 52 which is delivered to the baseof a transistor Q4 to turn on transistor Q4 when an incipient excessiveslip condition is detected.

The excessive slip detecting circuit 50 may be of the conventional typesuch as one which establishes a vehicle velocity analog signal uponapplication of the brakes and compares the actual speed of the slowestwheel with the vehicle velocity analog signal to determine whenexcessive slip is encountered. Alternatively, the excessive slipdetector 50 may be responsive to a wheel deceleration above a thresholdlevel which is indicative of an incipient excessive slip condition.Other forms and modifications of excessive slip detecting systems may beutilized. I

When transistor Q4 is turned on, the base of the normally conductingtransistor Q5, which is connected to the collector of transistor Q4 atterminal 54, is lowered to near ground potential so as to turn-off thetransistor 05. When transistor Q5 is non-conductive, the flow path ofcurrent from the battery terminal 26 through the brake actuators 22 and24 is interrupted thereby relieving brake actuation to allow theexcessively slipping wheel to spin up.

During spin-up of the excessively slipping wheel after the brakeactuation has been relieved, the circuit 44 continues to provide asignal which is representative of the speed of the slowest wheel. Solong as the slowest wheel is determined to be in an excessive slipcondition by the excessive slip detecting circuit 50, the transistor Q5will be maintained off so that full braking is not reinstated. Once theslowest wheel has spun up to a sufficient velocity so that a controlledslip condition exists, that condition is detected by the excessive slipdetecting circuit 50 which terminates the signal on line 52 so as toturn off the transistor Q4. Consequently, the transistor Q5 is turned onso that full braking, if dictated by the driver, is restored.

In view of the above explanation, it will be appreciated that the system10 relieves brake actuation during a period which begins when the firstwheel approaches an excessive skid condition and ends when the lastwheel spins up to a controlled slip condition. That mode of operationprovides the maximum stability for the towed vehicle.

While it will be apparent that the teachings herein are well calculatedto each one skilled in the art the method of making preferred embodimentof this invention, it will be appreciated that the invention issusceptible to modification, variation and change without departing fromthe proper scope of meaning of the subjoined claims.

What is claimed is:

1. In combination with a towed vehicle having at least two wheels:

brake means for said two wheels including at least one electricallyoperated brake actuator;

means for providing an electrical signal for operating said electricallyoperated brake actuator, said means including an electric brakecontroller for varying said electrical signal to vary brake actuation;

slip detecting means for detecting the occurrence of an undesirable slipcondition at any one of said two wheels and the termination of anundesirable slip condition at both of said two wheels for providing anelectrical slip control signal representative thereof; and

circuit means including a controlled conduction device which isresponsive to said electrical slip control signal for controlling saidelectrically operated brake actuator in a manner to relieve actuation ofthe braking of both of said two wheels by said brake means upon adetected undesirable slip condition at any one of said two wheels and toreinstate actuation of the braking of both of said two wheels upon thetermination of an undesirable slip condition at both of said two wheels,said circuit means interconnecting said electric brake controller, saidcontrolled conduction device and said electrically operated brakeactuator in a manner so that each of said electric brake controller andsaid controlled conduction device is effective to control operation ofsaid electrically operated brake actuator.

2. A combination of claim 1 wherein said electric brake controllercontrols the degree of actuation of said brake.

3. A combination of claim 2 wherein said electrically operated brakeactuator is an electromagnetic actuator.

1. In combination with a towed vehicle having at least two wheels: brakemeans for said two wheels including at least one electrically operatedbrake actuator; means for providing an electrical signal for operatingsaid electrically operated brake actuator, said means including anelectric brake controller for varying said electrical signal to varybrake actuation; slip detecting means for detecting the occurrence of anundesirable slip condition at any one of said two wheels and thetermination of an undesirable slip condition at both of said two wheelsfor providing an electrical slip control signal representative thereof;and circuit means including a controlled conduction device which isresponsive to said electrical slip control signal for controlling saidelectrically operated brake actuator in a manner to relieve actuation ofthe braking of both of said two wheels by said brake means upon adetected undesirable slip condition at any one of said two wheels and toreinstate actuation of the braking of both of said two wheels upon thetermination of an undesirable slip condition at both of said two wheels,said circuit means interconnecting said electric brake controller, saidcontrolled conduction device and said electrically operated brakeactuator in a manner so that each of said electric brake controller andsaid controlled conduction device is effective to control operation ofsaid electrically operated brake actuator.
 2. A combination of claim 1wherein said electric brake controller controls the degree of actuationof said brake.
 3. A combination of claim 2 wherein said electricallyoperated brake actuator is an electromagnetic actuator.